Variable event valvetrain operation during an engine start

ABSTRACT

A method for improving engine starting for an engine having a variable event valvetrain is described. According to one aspect of the description, valve timing is adjusted during a start to reduce engine emissions and fuel consumption.

The present application is a divisional of U.S. patent application Ser.No. 11/224,464, titled MANIFOLD PRESSURE CONTROL FOR A VARIABLE EVENTVALVETRAIN, filed Sep. 12, 2005, the entire contents of which areincorporated herein by reference in their entirety for all purposes.

FIELD

The present description relates to a method for controlling intakemanifold pressure for an internal combustion engine having a variableevent valvetrain.

BACKGROUND

One method to control valve timing of an internal combustion having avariable event valvetrain is described in U.S. Pat. No. 6,681,741. Thispatent describes several valve timing methods that may be used duringstarting of an engine having a variable event valvetrain. In particular,the different methods attempt to improve cylinder turbulence and reducefuel adherence to the intake port. The intake valves are initially setto open at a location that is before top-dead-center of the intakestroke of the cylinder in which the valve operates. After the enginespeed reaches a predetermined level the intake valve opening time isswitched to position that is after top-dead-center of the intake strokeof the cylinder. The intake valve opening remains at this location untila change in an operating condition causes the intake valve opening timeto return to a position before top-dead-center of the intake stroke.

The above-mentioned method can also have several disadvantages.Specifically, the cylinder air-fuel mixture may not mix as well asdesired when the engine is being cranked or when it is accelerating fromcrank speed up to the time it reaches a certain operating speed(run-up). Further, engine fuel consumption may be higher than desiredbecause the cylinder charge motion and air-fuel mixing may not besufficient at low engine speed to improve combustion. In other words,portions of the cylinder air-fuel mixture may combust less completelythan other portions of the cylinder air-fuel mixture due to lack ofhomogeneity of the air-fuel mixture. Further still, the method onlyappears to recognize that it is desirable to heat an exhaust aftertreatment device. The method does not appear to recognize that there areadditional benefits that can be achieved by quickly heating the engineand engine fluids.

The inventors herein have recognized the above-mentioned disadvantagesand have developed a method of controlling intake manifold pressure thatoffers substantial improvements.

SUMMARY

One embodiment of the present description includes a method to controlintake manifold pressure for an internal combustion engine having avariable event valvetrain, the method comprising: during an enginestart, after reaching a desired engine speed, operating an internalcombustion engine at a first intake manifold pressure and a first intakevalve opening duration; and reducing said intake manifold pressure byclosing a throttle located upstream of an intake manifold, andincreasing said first intake valve opening duration to produce a secondintake valve opening duration, in response to a predetermined engineoperating condition. This method overcomes at least some of thelimitations of the previously mentioned method.

By controlling intake manifold pressure and valve timing during a startit is possible to reduce engine emissions and fuel consumptions.Specifically, valve timing and manifold pressure can be adjusted duringa start to increase catalyst heating. Then, after the catalyst reaches adesired condition, valve timing and manifold pressure can be adjusted toincrease the heat transfer of combusted gases to the engine. Heating theengine quickly can reduce engine friction; thereby lowering fuelconsumption, at least during some conditions.

The present description may provide several advantages. In particular,the approach may reduce engine hydrocarbon emissions and fuelconsumption after an engine start. Further, the method may be used toimprove engine combustion stability when an engine is cold.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings,wherein:

FIG. 1 is a schematic diagram of an engine;

FIG. 2 a is an example timing diagram showing intake and exhaustmanifold pressure relative to intake and exhaust valve timing;

FIG. 2 b is a schematic diagram of a cylinder approaching the end of anexhaust stroke;

FIG. 3 is a flow chart of an example method to control intake manifoldpressure for an engine having a variable event valvetrain;

FIG. 4 is a plot showing signals of interest for one example of intakemanifold pressure control;

FIG. 5 is a plot showing signals of interest during an example startingsequence of an engine having a variable event valvetrain;

FIGS. 6 a and 6 b are plots that illustrate some signals of interestduring an example start of an internal combustion engine;

FIG. 7 is a plot of cylinder pressure during an induction stroke of aninternal combustion engine;

FIG. 8 is a schematic of an example electrically actuated valve; and

FIG. 9 is a flow chart of an example method to start an internalcombustion engine.

DETAILED DESCRIPTION

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is knowncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 an exhaust valve 54. Each intake and exhaustvalve is operated by an electromechanically controlled valve coil andarmature assembly 53. Alternatively, the intake 52 or exhaust 54 valvemay be mechanically actuated via a camshaft, for example. Further, amechanical device may be used to control valve lift and/or valve timing.Valve actuator armature temperature is determined by temperature sensor51. Valve position is determined by position sensor 50. Valve positionmay be determined by linear variable displacement, discrete, or opticaltransducers or from actuator current measurements. In an alternativeexample, each valve actuator for valves 52 and 54 has a position sensorand a temperature sensor. In yet another alternative example, armaturetemperature may be determined from actuator power consumption sinceresistive losses can scale with temperature.

Intake manifold 44 is also shown having fuel injector 66 coupled theretofor delivering liquid fuel in proportion to the pulse width of signalFPW from controller 12. Fuel is delivered to fuel injector 66 by fuelsystem (not shown) including a fuel tank, fuel pump, and fuel rail (notshown). Alternatively, the engine may be configured such that the fuelis injected directly into the engine cylinder, which is known to thoseskilled in the art as direct injection. In addition, intake manifold 44is shown communicating with optional electronic throttle 125.

Distributorless ignition system 88 provides ignition spark to combustionchamber 30 via spark plug 92 in response to controller 12. UniversalExhaust Gas Oxygen (UEGO) sensor 76 is shown coupled to exhaust manifold48 upstream of catalytic converter 70. Alternatively, a two-stateexhaust gas oxygen sensor may be substituted for UEGO sensor 76.Two-state exhaust gas oxygen sensor 98 is shown coupled to exhaust pipe73 downstream of catalytic converter 70. Alternatively, sensor 98 canalso be a UEGO sensor. Catalytic converter temperature is measured bytemperature sensor 77, and/or estimated based on operating conditionssuch as engine speed, load, air temperature, engine temperature, and/orairflow, or combinations thereof.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, andread-only-memory 106, random-access-memory 108, 110 Keep-alive-memory,and a conventional data bus. Controller 12 is shown receiving varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including: brake boost pressure (not shown); fuelvapor canister hydrocarbon concentration sensor (not shown); enginecoolant temperature (ECT) from temperature sensor 112 coupled to waterjacket 114; a position sensor 119 coupled to a accelerator pedal; ameasurement of engine manifold pressure (MAP) from pressure sensor 122coupled to intake manifold 44; a measurement (ACT) of engine air amounttemperature or manifold temperature from temperature sensor 117; and aengine position sensor from sensor 118 sensing crankshaft 40 position.Sensor 118 may be a variable reluctance, Hall effect, optical, ormagneto-resistive sensor. Alternatively, a camshaft position sensor mayalso be provided and may be used to determine engine position. In apreferred aspect of the present description, engine position sensor 118produces a predetermined number of equally spaced pulses everyrevolution of the crankshaft from which engine speed (RPM) can bedetermined.

Referring to FIG. 2 a, an example timing diagram that shows intake andexhaust valve timing relative to intake and exhaust port pressures. Thex-axis represents engine position and is displayed in units ofcrankshaft degrees. Two y-axes are also shown, the left indicatingpressure and the right indicating valve lift amount. The figure depictsa part load operating condition at a constant engine speed. However, theillustrated behavior can be observed during dynamic engine operatingconditions and is therefore not intended to limit the scope or breadthof the description.

Continuing with FIG. 2 a, line 202 illustrates exhaust port pressure.The exhaust pressure is shown fluctuating about an average pressure asthe engine rotates and cylinder contents are pumped into the exhaustport and manifold. The intake port pressure is represented by line 203and also fluctuates as the engine rotates and air is drawn from theintake port and manifold into the cylinder. Further, the amplitude ofthe pressure fluctuation can increase if the intake or exhaust system isexcited at its natural frequency, thereby setting the system intoresonance. In this example, the intake and exhaust pressures are shownapproximately 180° out of phase. That is, when one pressure reaches apeak the other pressure reaches a valley. If intake and exhaust valvesare simultaneously open during a period when one port pressure is higherthan the other, then the pressure differential can cause flow from oneport to the other. Line 204 represents intake port pressure when enginethrottling is increased beyond the level shown in line 203. Intakemanifold pressure may be lowered by reducing the throttle opening amountof throttle 125, for example. Further, under some conditions, a throttlemay be used to lower manifold pressure, but valve timing may be changedso that an equivalent cylinder air charge may inducted into a cylinder.For example, a cylinder air charge produced at a first throttle openingamount, an opening amount greater than a second throttle opening amount,may be produced at the second throttle opening amount by increasing theintake valve opening duration or by adjusting the valve opening timing.Of course, this relationship holds better when the engine is operated ata larger throttle opening and shorter duration valve timings and thentransitions to a smaller throttle opening and longer duration valvetimings.

Cylinder valve timing is shown by lines 205 and 208. Line 205 representsthe profile of a mechanically actuated exhaust valve while line 208represents an opening profile of an electrically actuated intake valve.Location 206 indicates intake valve opening and location 207 indicatesthe exhaust valve closing location. The intake and exhaust valves areopen during respective intake and exhaust strokes, but the exhaust valveopening extends into the intake stroke and the intake valve openingextends into the exhaust stroke. By extending the valve opening into theadjacent stroke, a period of valve overlap can be created aroundtop-dead-center of the intake stroke. Line 210 is used to illustrate thebeginning of valve overlap and line 212 illustrates the end of valveoverlap. During the period of valve overlap a pressure differential fromone port to the other can cause flow between the ports. For example, ifpressure in the intake port is higher than pressure in the exhaust portduring valve overlap, then the contents of the intake port may be pulledthrough to the exhaust port. Conversely, if pressure in the exhaust portis higher than pressure in the intake port during valve overlap, thenthe contents of the intake port may be pulled through to the intakeport.

It can be seen for at least a portion of the valve overlap period(between 210 and 212) that the intake pressure is shown at a higherpressure level than the exhaust pressure. The pressure differentialacross the cylinder can drive flow from the intake port to the exhaustport. Therefore, it is possible to draw at least a portion of theair-fuel mixture from the intake port directly to the exhaust portwithout having combusted the mixture. As mentioned above, this canreduce the efficiency of the engine and increase emissions ofhydrocarbons. On the other hand, when the engine is sufficientlythrottled upstream of the intake manifold the pressure in the intakemanifold may be lower than the exhaust manifold pressure. As a result,residuals may be pulled from the exhaust port into the cylinder, therebyallowing additional residuals to flow into a subsequent cylindermixture. By controlling the intake manifold pressure and valve overlapduration, scavenging between the intake manifold and exhaust manifoldcan be controlled.

Referring to FIG. 2 b, a schematic diagram of a cylinder approaching theend of an exhaust stroke is shown. Intake valve 52 and exhaust valve 54are shown open and in an overlap interval. If pressure in the intakemanifold is higher than that in the exhaust manifold then some portionof a non-combusted air-fuel mixture may be drawn from the intake port tothe exhaust port as illustrated by the two directional arrows, therebyincreasing hydrocarbon emissions. In contrast, if the exhaust manifoldpressure is higher than the intake manifold pressure exhaust gases mayflow from the exhaust port to the intake port in the direction oppositeto the arrows. It may be useful to draw residuals from the exhaustmanifold to the intake manifold so that internal EGR may be used tocontrol the combustion process in the cylinder. However, drawing an airfuel mixture from the intake manifold to the exhaust manifold mayincrease fuel consumption and emissions and therefore may not be asdesirable.

Referring to FIG. 3, a flow chart of an example method to control intakemanifold pressure for an engine having a variable event valvetrain isshown. In step 301, engine operating conditions may be determined byinterrogating sensor outputs or by inference. For example, barometricpressure can be determined by sensing manifold pressure sensor 122before engine rotation begins. Furthermore, engine speed, engine torquedemand, engine inlet air temperature, engine coolant temperature,cylinder air charge amount, and catalyst temperature may be determinedor inferred by interrogating respective sensors. The routine proceeds tostep 303.

In step 303, a desired manifold pressure can be determined. An engineoperating in a vehicle can have a variety of sources that may makedifferent operational demands on the engine. For example, an operatorcan demand an engine torque amount by depressing accelerator pedal 119or a control algorithm can request an engine operating point thatincreases fuel economy, adjusts brake boost pressure, reduces intake orexhaust manifold scavenging, increases engine or catalyst heating,adjusts crankcase ventilation, maintains a level of combustionstability, or changes volumetric efficiency via valve timing. Theseoperational demands may involve adjusting the intake manifold pressureto meet the requested demand. When various sources compete for controlof manifold pressure one way to arbitrate between them is to select therequest that demands the lowest manifold pressure so that several of therequests may be simultaneously served. Systems requesting manifoldpressure may use predetermined tables or functions to select a desiredintake manifold pressure. For example, canister purge may request amanifold pressure based on fuel tank pressure and time since the enginewas started, for example.

In one example, it may be desirable to reduce scavenging between theintake and exhaust manifolds. As mentioned above, scavenging from theintake manifold to the exhaust manifold can reduce engine power,increase hydrocarbon emissions, and reduce engine efficiency. On theother hand, scavenging from the exhaust manifold to the intake manifoldmay result in misfires if levels of EGR are higher than a particularamount. Since scavenging may be related to manifold pressure and to thefrequencies that excite mechanical system resonances, as illustrated byFIG. 2 a, scavenging may be controlled by scheduling manifold pressureas a function of engine speed and requested engine torque, for example.

In another example, manifold pressure can be scheduled to improve fuelefficiency by selecting a manifold pressure that provides an increasednet engine work. That is, manifold pressure can be selected where thesum of indicated efficiency and engine pumping work produces a higherlevel of net engine work. At some operating conditions engine pumpingwork may be reduced by opening the throttle so that intake manifoldpressure is at or near atmospheric pressure. At other engine operatingconditions it may be desirable to lower intake manifold pressure so thatindicated efficiency may be improved.

In yet another example, intake manifold pressure can be determined inresponse to engine temperature and/or catalyst temperature. Whencatalyst temperature is low the manifold pressure may be set nearatmospheric pressure so that heat and mass flow may be increased to thecatalyst. Alternatively, manifold pressure may be lowered to improvecombustion stability during operating states where the catalyst andengine temperature are low. Further still, if a catalyst is at operatingtemperature and the engine temperature is low, manifold pressure can bereduced and spark advanced so that heat of combustion can be readilytransferred to the engine and to engine coolant.

In still another example, intake manifold pressure may be scheduled inaccordance to demands of peripheral systems such as brake boost, fuelvapor purge, and/or crankcase ventilation. These systems may request aspecific manifold pressure that induces a certain flow rate from therespective system to the intake manifold or they may request a pressurethat can exert a desired force on an actuator, for example. The routineproceeds to step 305.

In step 305, the throttle plate can be adjusted to help control theintake manifold pressure. In one example, throttle position can bedetermined from the desired air flow rate through the engine andpressure drop across the throttle. The pressure drop across the throttlecan be determined by subtracting the desired manifold pressure from theambient air pressure. A table or function can be used to describe therelationship between throttle angle, pressure drop across the throttle,and throttle flow. For example, the x-axis index of a throttle angletable can be a pressure drop across the throttle and the y-axis indexcan be the desired air flow through the throttle. The table output isthrottle angle in degrees which corresponds to a throttle area. Inaddition, the throttle plate position may be corrected by determining anerror amount between actual and desired manifold pressure. The manifoldpressure error can then be used by a proportional/integral controller toopen or close the throttle plate so that the manifold pressure error maybe reduced. The routine proceeds to step 307.

In step 307, valve timing can be adjusted. In one example, the methoddescribed in U.S. patent application Ser. No. 10/805,642 can be used todetermine the intake valve timing and is hereby fully incorporated byreference. Specifically, a driver brake torque demand can be interpretedfrom pedal position sensor 119. The engine brake torque command can betransformed into individual cylinder pressure values and then intoindividual cylinder air and fuel amounts. Valve timing can be determinedfrom the individual cylinder air amounts.

The cylinder data can be transformed into cylinder pressure based on thefollowing regression equations A and B:PMEP _(Act) =C ₀ +C ₁ ·V _(IVO) +C ₂ ·V _(EVC) +C ₃ ·V _(IVC-IVO) +C ₄·N  Equation A:Where PMEP_(Act) is pumping mean effective pressure, C₀-C₄ are stored,predetermined, polynomial coefficients, V_(IVO) is cylinder volume atintake valve opening position, V_(EVC) is cylinder volume at exhaustvalve closing position, V_(IVC) is cylinder volume at intake valveclosing position, V_(IVO) is cylinder intake valve opening position, andN is engine speed. Valve timing locations IVO and IVC can be based onthe last set of determined valve timings.FMEP _(Act) =C ₀ +C ₁ ·N+C ₂ ·N ²  Equation B:Where FMEP_(Act) is friction mean effective pressure, C₀-C₂ stored,predetermined polynomial coefficients, and N is engine speed.

The following describes further exemplary details for the cylinderpressure regression and interpolation schemes. A one dimensionalfunction can be used to store friction and pumping polynomialcoefficients for cylinders. The data taken to determine the coefficientscan be collected at a sufficient number of engine speed points toprovide the desired torque loss accuracy. Coefficients can beinterpolated between locations where no data exists. For example, datacan be collected and coefficients are determined for an engine at enginespeeds of 600, 1000, 2000, and 3000 RPM. If the engine is then operatedat 1500 RPM, coefficients from 1000 and 2000 RPM can be interpolated todetermine the coefficients for 1500 RPM.

The losses based on pressure can then be transformed into torque by thefollowing equations:$\Gamma_{friction\_ total} = {{FMEP}_{Act} \cdot \frac{V_{D}}{4 \cdot \pi} \cdot \frac{N/m^{2}}{\left( {{1 \cdot 10^{- 5}}\quad{bar}} \right)}}$$\Gamma_{pumping\_ total} = {{PMEP}_{Act} \cdot \frac{V_{D}}{4 \cdot \pi} \cdot \frac{N/m^{2}}{\left( {{1 \cdot 10^{- 5}}\quad{bar}} \right)}}$The parameter V_(D) represents the displacement volume of enginecylinders. In addition, the fuel and air amount used by an engineoperating with less than a full complement of cylinders (e.g., sixcylinders of an eight cylinder engine) may also be determined byincluding the pumping and friction pressures of deactivated cylinders.

The desired indicated mean effective pressure (IMEP) for each cylindercan be determined, for example via the equation:${{IMEP}_{cyl}({bar})} = {\left( \frac{\Gamma_{brake} - \left( {\Gamma_{friction\_ total} + \Gamma_{pumping\_ total} + \Gamma_{accessories\_ total}} \right)}{Num\_ cyl} \right)*\frac{4\pi}{V_{D}}*{\frac{\left( {1*10^{- 5}\quad{bar}} \right)}{N/m^{2}} \cdot {SPKTR}}}$Where Num_cyl is the number of active cylinders, V_(D) is thedisplacement volume of active cylinders, SPKTR is a torque ratio basedon spark angle retarded from minimum best torque (MBT) (i.e., theminimum amount of spark angle advance that produces the best torqueamount). Additional or fewer polynomial terms may be used in theregression based on the desired curve fit and strategy complexity.Alternatively, different estimation formats can also be used. The termSPKTR can be based on the equation:${SPKTR} = \frac{\Gamma_{\Delta\quad{SPK}}}{\Gamma_{MBT}}$Where Γ_(ΔSPK) is the torque at a spark angle retarded from minimumspark for best torque (MBT), Γ_(MBT) is the torque at MBT. In oneexample, the actual value of SPKTR can be determined from a regressionbased on the equation:SPKTR=C ₀ +C ₁*Δ_(spark) ² +C ₂*Δ_(spark) ² *N+C ₃*Δ_(spark) ² *IMEP_(MBT)Where C₀-C₃ are stored, predetermined, regressed polynomialcoefficients, N is engine speed, and IMEP_(MBT) is IMEP at MBT sparktiming. The value of SPKTR can range from 0 to 1 depending on the sparkretard from MBT.

An individual cylinder fuel mass can be determined, in one example, foreach cylinder by the following equation:M _(f) =C ₀ +C ₁ *N+C ₂ *AFR+C ₃ *AFR ² +C ₄ *IMEP+C ₅ *IMEP ² +C ₆*IMEP*NWhere M_(f) is mass of fuel, C₀-C₆ are stored, predetermined, regressedpolynomial coefficients, N is engine speed, AFR is the air-fuel ratio,and IMEP is indicated mean effective pressure. Additional or fewerpolynomial terms may be used in the regression based on the desiredcurve fit and strategy complexity.

In one example, a predetermined air-fuel mixture (based on engine speed,temperature, and load), with or without exhaust gas sensor feedback,determines a desired air-fuel ratio. The determined fuel mass can bemultiplied by the predetermined desired air-fuel ratio to determine adesired cylinder air amount. The desired mass of air can be determinedfrom the equation:M _(a) =M _(f) ·AFRWhere M_(a) is the desired mass of air entering a cylinder, M_(f) is thedesired mass of fuel entering a cylinder, and AFR is the desiredair-fuel ratio.

Exhaust valve opening (EVO), intake valve open (IVO), and exhaust valveclose (EVC) timing can be determined from center point of overlap anddesired overlap. Center point of intake and exhaust valve overlap is areference point, in crank angle degrees, from where IVO and EVC aredetermined. Overlap is the duration, in degrees, that intake valves andexhaust valves are simultaneously open. IVO and EVC can be determined bythe following equations: ${IVO} = {{CPO} - \frac{OL}{2}}$${EVC} = {{CPO} + \frac{OL}{2}}$Where CPO is center point of overlap and OL is overlap. The location ofCPO and OL can be predetermined and may be stored in a table that isindexed by engine speed and air mass entering a cylinder. The amount ofoverlap and the center point of overlap can be selected based on desiredexhaust residuals and engine emissions.

Exhaust valve opening (EVO) can also be determined from a table indexedby engine speed and air mass entering a cylinder. The predeterminedvalve opening positions can be empirically determined and may be basedon a balancing engine blow down (i.e., exhaust gas evacuation) andlowering expansion losses. Further, the valve timings may be adjustedbased on engine coolant or catalyst temperature.

Since EVO, EVC, and IVO are scheduled in one example (i.e., predefinedlooked-up locations) intake valve closing (IVC) can be determined basedon these predetermined locations and the desired mass of air entering acylinder. The desired mass of air entering a cylinder can be translatedinto a cylinder volume by the ideal gas law:$V_{a} = \frac{M_{a} \cdot R \cdot T}{P}$Where V_(a) is the volume of air in a cylinder, M_(a) is a desiredamount of air entering a cylinder, R is a ideal gas constant, T is theintake manifold temperature, and P is the intake manifold pressure fromstep 303. By using the ideal gas law, individual cylinder volumes can beadjusted to provide the desired cylinder air amount at altitude.Furthermore, an altitude factor may be added to regression equations toprovide additional altitude compensation.

From the determined cylinder volume V_(a), a model-based regression canbe used to determine a relationship between a volume of air in acylinder and intake valve closing volume (IVC) from the equation:$V_{a} = {C_{0} + {C_{1}*\left( {V_{IVC} - V_{{Res}\backslash{Ti}}} \right)} + {C_{2}*{dV}_{Res}} + {C_{3}*\left( \frac{N}{1000} \right)*\left( {V_{IVC} - V_{{Res}\backslash{Ti}}} \right)} + {C_{4}*\left( \frac{N}{1000} \right)*{dV}_{Res}} + {C_{5}*\left( \frac{T_{i}}{T_{e}} \right)*\left( {V_{IVC} - V_{{Res}\backslash{Ti}}} \right)}}$Where V_(a) is the volume of air inducted into the cylinder, C₀-C₅ arestored, predetermined, regressed polynomial coefficients, V_(IVC) iscylinder volume at intake valve closed, V_(RES|Ti) is the residualvolume evaluated at the cylinder inlet temperature, dV_(res) is aresidual pushback volume, i.e., the volume of exhaust residuals enteringthe intake manifold, N is engine speed, T_(i) is intake manifoldtemperature, and T_(e) is exhaust manifold temperature. Additional orfewer polynomial terms may be used in the regression based on thedesired curve fit and strategy complexity. The unknown value of V_(IVC)can be solved from the above-mentioned regression to yield:$V_{IVC} = {V_{{Res}\backslash{Ti}} + \frac{\left( {V_{a} - C_{0} - {\left( {C_{2} + {C_{4} \cdot \frac{N}{1000}}} \right) \cdot {dV}_{Res}}} \right)}{C_{1} + {C_{3} \cdot \frac{N}{1000}} + {C_{5} \cdot \left( \frac{T_{i}}{T_{e}} \right)}}}$The solution of V_(IVC) is further supported by the following equationsderived from cylinder residual estimation:$V_{Res} = {V_{EVC} + \frac{\left( {V_{IVO} - V_{EVC}} \right)}{\left\lbrack {1 - {\left( \frac{V_{E}}{V_{I}} \right) \cdot \left( \frac{A_{E}}{A_{I}} \right)}} \right\rbrack}}$dV_(Res) = V_(Res) − V_(TDC)$V_{{Res}\backslash{Ti}} = {V_{Res} \cdot \left( \frac{T_{i}}{T_{e}} \right)}$$\frac{V_{E}}{V_{I}} = \sqrt{\frac{P_{m} + 1}{2}}$$V_{TDC} = \frac{v_{Dcyl}}{\left( {{CR} - 1} \right)}$${V(x)} = {\pi \cdot r^{2} \cdot \left( {L + \frac{s}{2} - {\frac{s}{2} \cdot {\cos(\Theta)}} - \sqrt{L^{2} - \left( {\frac{s}{2} \cdot {\sin(\Theta)}} \right)}} \right)}$

Where V(x) is the cylinder volume at crank angle Θ relative to top deadcenter of the respective cylinder, L is the length of a connecting rod,s/2 is the crank shaft offset where the connecting rod attaches to thecrankshaft, relative to the centerline of the crank shaft, r is thecylinder radius, CR is the cylinder compression ratio, V_(Dcyl) iscylinder displacement volume, V_(TDC) is cylinder volume at top deadcenter, V_(E)/V_(I) is the air velocity ratio across exhaust and intakevalves, A_(E)/A_(I) is the area ratio across exhaust and intake valves,V_(Res) is the residual cylinder volume, V_(IVO) is cylinder volume atintake valve opening, V_(EVC) is cylinder volume at exhaust valveclosing, and V_(TDC) is cylinder volume at top dead center. Thus,cylinder volumes V_(EVC) and V_(IVO) can be determined by solving forV(x) at the respective EVC and IVO crank angles. Further, crank angle Θcan be solved where V(x)=V_(IVC) to determine the location of IVC. Valvecontrol commands can be output to electrical and/or mechanical valveactuators so that the desired cylinder air amount may be inducted. Theroutine proceeds to step 309.

In step 309, spark timing can be adjusted. In one example, spark timingcan be determined by indexing one or more predetermined tables of sparkangle command amounts. The final spark may be determined by summing theoutput of several tables that can be indexed by engine speed, enginetemperature, air charge temperature, and the amount of air in acylinder, for example. After commanding the desired spark angle theroutine exits.

Referring to FIG. 4, a plot of signals for one example of intakemanifold pressure control is shown. The figure illustrates an example ofmanifold pressure control using the method of FIG. 3 when asubstantially constant driver torque demand is requested as engine speedis varied. That is, the manifold pressure is varied as engine speedvaries. This type of strategy can allow an engine controller to controlintake and exhaust manifold scavenging in an engine having a variableevent valvetrain. Similar conditions may be encountered during shifting,for example.

The figure shows that when the engine is operating at speeds below 1200RPM and above 1800 RPM the intake manifold pressure (subplot (a)) isheld substantially constant. Between 1200 RPM and 1800 RPM the manifoldpressure is reduced to control scavenging between the intake and exhaustmanifolds, for example. However, scavenging and other engine speeddependencies that may be influenced by intake manifold pressure mayoccur at different engine speeds for different engines, therefore thespeed range shown is for illustration purposes only and is not meant tolimit the scope or breadth of the description. Also, it is possible,although not shown in this example, to vary manifold pressure inresponse to fuel efficiency, brake boost, crankcase ventilation, andfuel vapor purge requests, for example.

The intake manifold pressure can be adjusted by changing the throttleposition (subplot (c)) and/or intake valve timing (subplot (b)). As thethrottle position is reduced, altering the density of air in the intakemanifold, intake valve opening duration may be increased so that theinducted cylinder air amount remains substantially constant.Alternatively, the intake valve timing and/or timing and openingduration may be altered so that the cylinder air amount remainssubstantially constant.

The dashed lines in each of the subplots represent example adjustmentsfor altitude compensation. At altitude, the pressure in the exhaustmanifold may be lower so that scavenging between the intake and exhaustmanifold may begin at a lower intake manifold pressure. Therefore, ataltitude the intake manifold pressure can be adjusted to compensate forthe lower exhaust pressure.

Note: intake valve timing and duration may be adjusted to reduce theinfluence of volumetric efficiency on the inducted cylinder air chargeas well as to compensate for throttling.

Referring to FIG. 5, a plot showing signals of interest during anexample starting sequence of an engine having a variable eventvalvetrain is shown. Vertical lines T₀-T₄ represent different phases ina starting sequence. The duration of the respective intervals may changein response to engine operating conditions and are shown forillustration purposes only and are not meant to limit the scope orbreadth of the description. The lines extend through all five subplotsso that the relationships between signals can be shown.

The trajectory of engine speed is shown in subplot (a). The sequencebegins a T₀ where the engine is stopped. Between T₀ and T₁ enginecranking and fuel delivery (not illustrated) commence, in response to arequest to start the engine at location 506. The engine beginscombustion and accelerates up to operating speed (run-up) between T₁ andT₂. Between T₂ and T₃ the engine is operated at an elevated speed sothat an increased amount of heat may be transmitted from the engine to acatalyst. The efficiency of a catalyst may be increased by providingheat to the catalyst, at least under some conditions. From T₃ to T₄ theengine is operated so that engine speed is elevated and so that heatfrom combustion may be more readily transferred to the engine and enginecoolant. In other words, the number of combustion events can beincreased over a time interval so that the engine and/or catalyst may bemore rapidly heated. In this way, the engine can be operated so thatheat from combustion may first warm a catalyst, thereby reducingemissions, and then the combustion heat may be used to warm the engine,thereby improving engine fuel efficiency, reducing feed gas emissions(combustion products exhausted from the cylinders), and improving cabinwarm-up. After T₄ the engine speed can be reduced and the engineoperated so that the net work of the engine may be improved.

Subplot (b) shows the progression of manifold pressure throughout theexample start sequence. Initially, manifold pressure is at an elevatedlevel indicating that the manifold may be at or near atmosphericpressure. The figure shows that as the engine speed increases, manifoldpressure falls. The pressure drop may be due to the air cleaner and/orrestrictions within the air induction system, for example. During thecatalyst warming period (T₂-T₃) manifold pressure stabilizes at apressure near ambient pressure so that the inducted cylinder air amountcan be elevated. By increasing the cylinder air amount and the enginespeed, the mass (combusted fuel and air mixture) flow rate of heatedexhaust gas encountering the catalyst can be increased, therebyincreasing the heating of the catalyst. The time duration between T₂ andT₃ may be determined by a timer, driver demand torque, a catalysttemperature model, or by the output of a temperature sensor located inor near the catalyst. Between T₃ and T₄ the manifold pressure is loweredto improve combustion stability while the engine temperature isincreasing. The lower intake manifold pressure allows the spark to befurther advanced so that the cylinder temperature may be increased.After T₄ the manifold pressure may be controlled to a value where engineefficiency may be increased, for example.

Spark advance during this example start is illustrated by subplot (c).Spark in the + direction represents spark in advance of TDC compressionwhile spark in the − direction represents spark retarded from TDCcompression. The figure shows spark being set to a predetermined valuein response to a request to start the engine. During engine run-up sparkcan be retarded as the engine speed increases so that spark and valvetiming, including opening duration, may be used to control engine torqueduring run-up. Between times T₂ and T₃ the engine reaches a desiredoperating idle speed where the mass flow rate through the engine isincreased above nominal idle conditions. The mass flow can be increasedby increasing the inducted air mass and by elevating the engine idlespeed. Engine torque can be controlled during this increased mass flowrate region by retarding the spark after TDC as shown in the figure.After the catalyst is heated to a desired temperature the spark can beadvanced to the engine knock limit or until a level of engine torque isproduced by the desired air mass, between T₃ and T₄ for example. Byadvancing the spark, combustion can be initiated earlier in the cylindercycle, thereby increasing the time the combusted gases are in thecylinder. Further, the exhaust valve opening time may be retarded (e.g.,beyond bottom-dead-center (BDC) of the exhaust stroke) to extend thetime heat can be transferred from combusted gases to the cylinder wallsand to the engine. Beyond T₄ spark can be adjusted to increase netengine torque, in one example, or spark can be adjusted to a positionretarded from minimum spark for best torque (MBT) so that spark can beadvanced or retarded to control engine idle speed, for example.

Subplot (d) shows engine valve timing being adjusted during a start sothat combustion stability (one measure of combustion stability is thestandard deviation of IMEP) and engine feed gas emissions may beimproved. From T₀ to T₁ the exhaust timing can be held fixed. In oneexample, the exhaust valves are held closed until a first combustionevent in the cylinder, and then the exhaust valve is opened early (e.g.,in the range between 90° and 140° ATDC compression stroke) to increasethe heat released to the catalyst. During this same period, the intakevalve opening can be retarded in the range of 50°-120° ATDC of theintake stroke, for example. During engine run-up from T₁ to T₂ theintake valve opening time can be varied as a function of engine speed.This valve timing adjustment can be done to improve the cylinder airamount consistency and the charge motion of inducted air charge as theengine speed changes. For example, during late intake valve opening, apressure differential can be created between the cylinder and the intakemanifold. When the intake valve opens a near step change in flow acrossthe intake valve can occur. Consequently, the pressure in the cylinderincreases and can form a damped oscillatory response until the intakevalve closes or until the higher frequency pressure oscillations aredamped, see FIG. 7 for example. The frequency and rate of damping of thedamped oscillatory response may be related to the motion of the pistonwhich can be related to the speed of the engine. By adjusting the intakevalve opening or closing position as a function of engine speed, theamount of air inducted into the cylinder can be controlled since thevalve closing position may be made coincident with a desired cylinderpressure, even when the cylinder pressure is oscillating. Between T₂ andT₄ the valve opening location is shown continuing to change as enginespeed changes. Alternatively, as mentioned above, the intake valveclosing position may be changed with engine speed. After time T₄ theintake valve timing can be moved from late intake valve opening to anearlier timing, namely before TDC of the intake stroke. In addition, theillustrated valve timings represent valve timings when the engine isstarted at a specific engine temperature. However, the valve timings canalso vary with engine temperature so that combustion stability andair-fuel mixing may be improved. In this way, the intake valve timingscan change from one start to another start. Between T₀ and T₄ theexhaust valve timing can be set so that there is no overlap between theintake valve and the exhaust valve. This can allow the vacuum in thecylinder to be increased so that fuel vaporization may be improved.Alternatively, the exhaust valve timing may be such that positive valveoverlap occurs when intake valve timing is set late. This can increasethe time the exhaust gases are in the cylinder and may improve enginetorque and/or efficiency.

In subplot (e) throttle position is shown. The x-axis represents aclosed or minimal throttle position where the throttle opening area isreduced. A wide open throttle (WOT) position is identified next to theY-axis to establish an upper bound of throttle position. From T₀ to T₃the throttle position is shown substantially constant, except duringinitialization when the throttle can be pre-positioned from a closedposition to an open position that may be based on barometric pressure,desired engine speed, desired engine torque, desired engine output heat,engine temperature, and ambient air temperature, for example.Alternatively, the throttle may be positioned in response tocombinations and/or sub-combinations of the previously mentionedparameters. Further, the throttle preposition can range from the closedposition to the WOT position depending on the throttle positioncalibration and/or strategy. Further still, throttle position can becontrolled in response to engine events. For example, during an enginestart the intake manifold pressure can change in response to the numberof intake or induction events. By moving the position of the throttle inresponse to a number of engine events it may be possible to controlmanifold pressure so that it follows a desired trajectory or so that itremains substantially constant because the pressure in the intakemanifold can be related to the outgoing (inducted air mass) and incoming(from the throttle) air mass. In one example, the throttle can bepositioned in response to the counted number of intake strokes orinduction events. The throttle command can be stored in a table indexedby the number of induction events or the throttle position may be theoutput of a discrete model having throttle commands that may be updatedfor each engine event. Of course, the type of engine event is notlimited to induction events, and may include other types of enginerelated events such as combustion events, spark events, or exhaustevents for example. After a predetermined number of events the throttleposition control can be transitioned to a known method of throttlecontrol (e.g., throttle position based on engine speed and desirecylinder air charge). In yet another example, the event based throttlecontrol may update the throttle command in response to the observedmanifold pressure during a start. In other words, during enginestarting, at each throttle position update (at each engine event) theintake manifold pressure can be compared to a desired manifold pressure.If the manifold pressure varies by more than a predetermined amount thenthe throttle position may be updated by adjusting model parameters or byadjusting command values stored in the before-mentioned throttle table.In this way, any manifold pressure errors observed during a currentengine start can be compensated during a subsequent engine start byadjusting the event based throttle commands. It is also possible toadjust the throttle position as a function of ambient temperature and/orpressure from modeling or empirically determined data so that throttleposition may be adjusted by a multiplier, for example.

Continuing with FIG. 5, in the period from T₃ to T₄ the throttle openingcan be reduced so that the intake manifold pressure may be reduced toimprove combustion stability during the engine heating period. After T₄the throttle opening can be increased so that engine pumping work may bereduced.

Between T₀ and T₄ the engine may be operated using late intake valveopening and a lean air-fuel mixture so that emitted hydrocarbons may bereduced and so that the amount of time it takes for a catalyst to reachoperating temperature may be reduced. After the catalyst and/or enginereach a desired operating temperature the engine air-fuel ratio may goto a stoichiometric air-fuel mixture.

Note: It is possible for an operator to request torque during a startwhich may alter the starting sequence. For example, if the operatorattempts to drive away between T₂ and T₃ spark can be advanced and thevalve timing may be adjusted to an earlier timing (e.g., before TDCintake), in response to the driver torque request, so that the enginetorque may be increased to accelerate the vehicle. Further, the throttleposition and manifold vacuum may be controlled to provide a desiredportion of combustion energy to catalyst heating and another portion ofcombustion energy to engine torque generation. Further still, theillustrated timing sequences are one example and are not intended tolimit the scope or breadth of the present disclosure. For example, thetime between T₂ and T₃ may be increased or decreased in response toengine operating conditions.

Referring to FIG. 6 a, is a plot that illustrates some signals ofinterest during an example start of an internal combustion engine. Inparticular, intake and exhaust valve timing for a simulated start of afour cylinder engine is shown. In addition, the position of a throttleplate located upstream of an intake manifold is also shown.

The figure shows example signals for an engine having electricallyactuated intake valves and mechanically actuated exhaust valves.However, it is also possible to provide similar valve sequences withelectrical actuated intake and exhaust valves, or using mechanicallyactuated intake and exhaust valves that are designed to be deactivatedin an open or closed position. Intake valve timing sequences are labeledI1-I4 and exhaust valve timing sequences are labeled E1-E4. The timingof the x-axis for each cylinder valve event is illustrated in enginerotational degrees relative to top-dead-center of the compression strokeof the respective cylinder.

At time T₀ a request to start the engine is initiated by the driver orby a vehicle system (e.g., a hybrid powertrain control module). At thistime, the electrically actuated valves are shown being commanded from adeactivated neutral position to an open position. However, someelectrically actuated valve designs may place valves in an open orclosed position when deactivated, but irrespective of the deactivationstate, the valves can be commanded to a partially or fully open state.Further, the intake valve may remain in a neutral mid position until theintake stroke of the respective cylinder occurs, or alternatively, thevalve may be opened after a time or engine rotation delay (i.e., openedafter a number of cylinder strokes or crank angle degrees).

Continuing with FIG. 6 a, cylinder one intake valve is shown being heldopen during the first possible intake stroke of cylinder one. Thisexample illustrates valve timing for an engine controller that may notbe capable of initially recognizing the position of the engine. In otherwords, the engine position sensors may not provide sufficientinformation to determine the position of the engine until a certainamount of engine rotation has occurred, for example. On the other hand,this figure can also illustrate that the engine controller may havedetermined that there may be an insufficient amount of time to injectfuel before the compression stroke is reached or that insufficientengine speed, that may be necessary for fuel vaporization, is present,for example. These conditions may occur for a port fuel injected engine.Therefore, the intake valve of cylinder one is shown held open until thesecond intake stroke of cylinder one occurs. In this example, the intakevalve can be held open until some time during the intake or compressionstroke. By holding the intake valve in an open position at least aportion of any residual hydrocarbons in the cylinder may be pushed intothe intake manifold, instead of into the exhaust manifold. Consequently,the hydrocarbons expelled into the intake manifold may be subsequentlycombusted during a later combustion event so that tailpipe emissions maybe reduced.

The dashed line illustrates an alternate example valve sequence wherethe intake valve can be closed prior to capturing a first air amountduring an intake stroke that may be scheduled for combustion. Observethat the intake valves can and are being shown operating with andwithout regard to the position of the mechanically actuated exhaustvalves, depending on control objectives. Specifically, before combustionbegins (combustion is initiated by spark and is illustrated by *) intakevalves are controlled without regard to engine position so that enginepumping work may be reduced and so that the amount of hydrocarbonsexpelled into the exhaust may be reduced. As previously mentioned, theintake valve timing for the respective cylinders can be determinedrelative to the exhaust valve timing for the respective cylinder. Thatis, since the exhaust valves are mechanically driven they have apredetermined relationship with the engine crankshaft position. Thisrelationship can define the cycle of the cylinder. Therefore, at leastduring some conditions, it may be desirable to link the intake valveoperation with the exhaust valve operation. That is, if a four strokecylinder cycle is desired, it can be desirable to operate (open and/orclose) the intake valve relative to the opening of an exhaust valveoperating in four stroke cycle.

The valve timing for the remaining cylinders, cylinders 2-4, are shownfor completeness. Valve timing for these cylinders is similar to thatshown for cylinder one, but is moved in relation to the crankshaftposition to smooth engine operation. In addition, the starting positionof the engine can be arbitrary so that the duration of intake valveopening from start to start may vary between cylinders. That is, thetiming illustrated in FIG. 6 a is not meant to limit the scope orbreadth of the description, but is one example of the valve timingstrategy described herein. For example, during a first start cylindernumber one intake valve may be open for three piston strokes whilecylinder number three intake valve may be open for four piston strokes.During a second start, cylinder number one intake valve may be open forfour strokes and cylinder number three intake valve may be open for onestroke.

The alternate valve timings and alternate types of fuel injection (e.g.,port or direct) make it possible to provide several different fueldelivery methods. At location 601, a port injected engine may beconfigured to inject fuel on a close valve. This fuel injection timingmay improve fuel vaporization during some conditions. Location 602illustrates open valve injection for a port fueled engine. This fuelinjection timing may improve charge mixing and fuel vaporization duringsome conditions. Location 603 illustrates an example of fuel deliverytiming for a fuel charge that may be directly injected into a cylinder.Of course, these injection options may be available for subsequentcombustion cycles of cylinder one and for the other cylinders as well,but are not illustrated. Valve timing and injection timing for theremaining cylinders follow the same pattern as that shown for cylinderone.

To further improve starting, intake valve timing is shown opening latein the intake stroke. That is, the intake valve opens at a crankshaftangle between 45° and 120° after top-dead-center of the intake stroke.The opening of the late opening intake valve timing can be varied asengine speed varies. Alternatively, the valve closing position may bevaried as engine speed varies. Adjusting the valve timing in relation toengine speed can be useful during a start since the response of the airentering the cylinder can vary as described above. This valve sequencecan increase combustion stability and may improve fuel vaporization.

Throttle position is shown at the lower trace signal in FIG. 6 a, (TP).In response to the request to start the engine the throttle can be movedfrom a closed position to an open position. The throttle can be closedinitially so that evaporative emissions of the engine may be reducedduring the period when the engine is not operating. By opening thethrottle and intake valves, hydrocarbons from the cylinder may beallowed to displace fresh air in the intake system. The vapors in theintake manifold may subsequently be inducted into the cylinder andcombusted as the cylinders begin to operate. The throttle can be openedto reduce the intake manifold restriction while the pistons are pumpingso that more hydrocarbons are allowed to flow into the intake manifold.

Spark timing is denoted by an * in FIG. 6 a. Initially the spark timingis advanced to a position before top-dead-center and then is moved aftertop-dead-center during subsequent cylinder events. This spark timing canhelp to initially accelerate the engine. As engine speed reaches apredetermined value the spark can be retarded to control engine speedand emissions. Alternatively, spark may be retarded from the beginningof the sequence and the duration of the valve timing varied to controlcylinder torque. For example, the intake valve opening duration and theintake valve opening or closing position may be adjusted during a startso that engine torque may be controlled.

Referring to FIG. 6 b, is a plot that illustrates some signals ofinterest during an example start of an internal combustion engine. Thesignals, signal labels, and engine timing references are similar tothose illustrated in FIG. 6 a, but this figure illustrates timing for anengine controller that can memorize the engine stopping position or thatmay be able to determine engine position before engine rotation begins.Because engine position may be known from the start, engine intakevalves may be operated right in sequence with the mechanically drivenexhaust valves. Cylinder number one for example, closes the intake valvein sequence with the mechanically drive exhaust valve of cylinder numberone.

As described above, depending on the fuel injection method (e.g., portinjection or direct injection) fuel may be injected on an open valve,closed valve, or directly into the cylinder when valves are closed.Label 604 shows injection on an open or closed valve. That is, dependingon control objectives, the intake valve may be opened or closedfollowing the request to start the engine. At label 605, fuel injectionis shown when the intake valve is closed. This can be accomplished byinjecting fuel directly into the cylinder. Further, the engine may bedirectly started such that a starter may not be required to start theengine. Namely, the fuel may be injected while the intake and exhaustvalves are closed and then the air-fuel mixture may be combusted so thatthe increased cylinder pressure causes the engine to rotate. Asdescribed above, it is not necessary for the engine to start from thelocation illustrated in FIG. 6 b, rather the engine may be started fromany stopped position using the cylinder exhaust valve opening positionas the reference to determine the first cylinder to combust during thestart sequence.

Referring to FIG. 7, a plot of cylinder pressure during an inductionstroke of an internal combustion engine is shown. Specifically, twopressure signals from two separate induction strokes are shown. Thex-axis has units of crankshaft angle degrees measured relative totop-dead-center of the intake stroke. The y-axis has units of pressuremeasured in bar. Each of the intake valves are opened late in the intakestroke. That is, they are opened after top-dead-center of the intakestroke. Signal 901 shows cylinder pressure during an intake stroke of anengine operating at a speed of 1000 revolutions per minute (RPM). Signal902 is similar to signal 901, but the intake valve is opened later, atapproximately 115° and at an engine speed of 200 RPM. Each pressuretrace begins from top-dead-center where cylinder pressure is nearly thesame as atmospheric pressure. As the piston moves away fromtop-dead-center the cylinder pressure is reduced until the intake valveopens. The opening valve causes cylinder pressure to increase and thesystem response produces a damped pressure oscillation in the cylinder.The pressure responses have a similar shape but the rate of oscillationwith respect to crankshaft position appears to be higher for the 902(200 RPM) signal. However, the plot is expressed in terms of crankshaftdegrees. If the signals are reviewed in terms of frequency content theyare similar. Thus, by moving intake valve opening with respect to enginespeed, the peaks and valleys can be moved so that a desired cylinderpressure is present at intake valve closing. On the other hand, it isalso possible to move intake valve closing with respect to engine speedso that a desire cylinder air charge may be inducted.

Referring to FIG. 8, a schematic of an example electrically actuatedvalve is shown. The valve actuator is shown in a de-energized or neutralstate (i.e., no electrical current is being supplied to the valveactuator coils). The electromechanical valve is comprised of an armatureassembly and a valve assembly. The armature assembly is comprised of anarmature return spring 801, a valve closing coil 805, a valve openingcoil 809, an armature plate 807, a valve displacement transducer 817,and an armature stem 803. When the valve coils are not energized thearmature return spring 801 opposes the valve return spring 811, valvestem 813 and armature stem 803 are in contact with each other, and thearmature plate 807 is essentially centered between opening coil 809 andclosing coil 805. This allows the valve head 815 to assume a partiallyopen state with respect to the port 819. When the armature is in thefully open position the armature plate 807 is in contact with theopening coil magnetic pole face 826. When the armature is in the fullyclosed position the armature plate 807 is in contact with the closingcoil magnetic pole face 824.

Referring to FIG. 9 a flow chart of an example starting sequence isshown. The method described in FIG. 9 may be used to achieve thestarting sequences illustrated in FIGS. 5, 6 a, and 6 b. In step 901,engine operating conditions may be determined by interrogating sensorinputs or by inference. For example, engine speed, engine torque demand,engine inlet air temperature, engine coolant temperature, barometricpressure, cylinder air charge amount, and catalyst temperature may bedetermined or inferred by interrogating respective sensors. The routineproceeds to step 903.

In step 903, the routine determines if there is a request to start theengine. If so, the routine proceeds to step 905, if not, the routineproceeds to exit.

In step 905, the throttle located upstream of the intake manifold isopened and intake valves may be positioned for an impending start. Thethrottle can be moved from a closed position where it may be placed whenthe engine is stopped. The throttle can be set closed so thathydrocarbons in the engine may be trapped in the engine instead ofallowing them to escape into the atmosphere. Further, opening thethrottle may allow the cylinder volume to displace some of the intakemanifold volume without significantly increasing the intake manifoldpressure. By keeping the manifold pressure low, a low impedance path maybe created between the cylinder and the intake manifold so thathydrocarbons may flow into the intake manifold rather than the exhaustmanifold. In this way, hydrocarbons may be held in the engine until theycan be combusted so that engine emissions may be reduced.

Intake valves may also be opened in step 905 so that hydrocarbon flow tothe exhaust may be reduced before combustion is initiated in individualcylinders. As mentioned above, opening the intake valve may create a lowrestriction path into the exhaust manifold so that as the pistonapproached top-dead-center more of the cylinder volume may be displacedto the intake manifold rather than the exhaust manifold. The intakevalves can be held open until a compression or exhaust stroke of arespective cylinder or the valve may be held open until the intakestroke or an early position in the compression stroke. By closing theintake valve during the compression or exhaust stroke the fuel may beinjected on to a closed intake valve. On the other hand, holding theintake valve open until the intake or early part of the compressionstroke allows open valve injection. Open valve or closed valve injectionmay be selected in response to engine operating conditions, for example.

The engine may begin to rotate with the assistance of a starter motor instep 905 or may be delayed until another step of the routine. However,if a particular engine controller is capable of determining engineposition without rotating the engine, additional valve positioning maybe provided before the engine begins to rotate. For example, for anengine controller that stores the engine stopping position in memory orthat can determine engine position without rotating the engine, someintake valves may be closed while others may be set to the held open orpartially open position before engine rotation and held open until anintake stroke of a first combustion event in the respective cylinder.The routine proceeds to step 907.

In step 907, engine position can be determined. As mentioned above, someengine control systems may determine engine position while the engine isstopped while others may need to monitor engine position signals as theengine rotates to determine engine position. By determining engineposition, the exhaust valve opening events of the cam driven valves mayalso be determined since the exhaust valves open based on camshaftposition and exhaust valve actuator command, unless the exhaust valveshave been mechanically deactivated. The engine controller may then alignintake valve opening events relative to the mechanically driven exhaustvalve events. The routine proceeds to step 909.

In step 909, the operation of the intake valves may be adjusted. Theengine operating conditions determined in step 901 can be used to adjustthe intake valve timing and/or opening duration. For example, if theengine and/or exhaust system are below predetermined temperatures, theintake valve timing may be retarded so that the intake valve opens aftertop-dead-center of the intake stroke. In addition, the valve opening andclosing positions may be further influenced by engine speed, barometricpressure, and driver torque demand, for example. The routine continuesto step 911.

In step 911, the intake valves can be operated relative to themechanically actuated exhaust valve timing. That is, after the engineposition and respective exhaust valve opening position are determinedthe intake valves may be operated so that the cylinders operate in apredetermined stroke (e.g., two-four-six stroke) mode. In one example,the intake valves can be opened while the engine is rotating and theengine controller is determining engine position, and then after engineposition is determined the intake valves can begin to operatesynchronously with the exhaust valves. This sequence can allow theengine controller to determine engine position while reducing engineemissions. The routine proceeds to step 913.

In step 913, the routine determines if the engine has started. Onemethod to determine if the engine has been started can be to compare thecurrent engine speed to a predetermined value. For example, the enginecranking speed can be below a reference speed that represents a startedengine. When the engine speed exceeds the reference speed the engine maybe determined to be started. Further, the method may determine that theengine is running up (i.e., accelerating from cranking speed tooperating speed) by determining that the engine speed is above thecranking or start speed but below the engine operating speed. If theengine is determined to be started the routine proceeds to step 915, ifnot, the routine waits until the engine is started or until the engineis requested to stop which can cause also cause the routine to exit.

In step 915, the engine and valves can be operated in response to engineoperating conditions. In one example, the timing of the late intakevalve opening can be varied with engine speed as the engine runs up andreaches operating speed. By adjusting the intake valve opening position,the intake valve can be used to compensate for pressure oscillation inthe cylinder that may be caused by late intake valve opening.Alternatively, the intake valve closing location may be adjusted withrespect to engine speed during engine run-up and cold idle. In addition,the valve opening timing may be adjusted in response to changes inbarometric pressure. Further still, the intake valve timing can beadjusted for changes in engine temperature and catalyst temperature.Specifically, the intake valves can be transitioned from late opening toearly opening after the engine and/or catalyst reach a predeterminedtemperature, for example.

Engine spark advance, throttle position, engine speed, and manifoldvacuum can also be controlled with respect to valve timing and otherengine operating conditions. Specifically, during a start where theengine temperature is below operating temperature, the engine controllercan operate the engine so that heat to the catalyst increased and sothat heat to the engine is increased. One embodiment is shown in FIG. 5,for example. The routine then exits.

Note: as previously mentioned different valve operating methods may besubstituted for the example electrically actuated intake andmechanically actuated exhaust valves. The alternative valve types may beused with respect to the method of FIG. 9 such that the description ofelectrically actuated intake valves and mechanically actuated exhaustvalves are used for illustration purposes and not intended to limit thescope or breadth of the description.

Thus, intake valve timing can be adjusted at the beginning of starting,for at least a portion of cylinders, without respect to exhaust valvetiming and then subsequently adjusted with respect to exhaust valvetiming. This can allow the engine controller to reduce engine emissionsby reducing hydrocarbons that may be pumped into the exhaust systemprior to combustion in a respective cylinder. For example, an engine maystop at a position where one cylinder is approaching or is on an exhauststroke. If the intake valve of the cylinder were closed during thisperiod, any residual hydrocarbons in the cylinder may be pumped from thecylinder to the exhaust. By opening the intake valve before or duringthe exhaust stroke, before a first combustion event in the cylinder,fewer hydrocarbons may be pumped into the exhaust.

As will be appreciated by one of ordinary skill in the art, the routinedescribed in FIGS. 3 and 9 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features and advantagesdescribed herein, but is provided for ease of illustration anddescription. Although not explicitly illustrated, one of ordinary skillin the art will recognize that one or more of the illustrated steps orfunctions may be repeatedly performed depending on the particularstrategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage.

1. A method to control intake manifold pressure for an internalcombustion engine having a variable event valvetrain, the methodcomprising: during an engine start, after reaching a desired enginespeed, operating an internal combustion engine at a first intakemanifold pressure and a first intake valve opening duration; andreducing said intake manifold pressure by closing a throttle locatedupstream of an intake manifold, and increasing said first intake valveopening duration to produce a second intake valve opening duration, inresponse to a predetermined engine operating condition.
 2. The method ofclaim 1 wherein said predetermined operating condition is an operatingcondition of an exhaust gas treatment device.
 3. The method of claim 2wherein said exhaust gas treatment device is a catalyst.
 4. The methodof claim 1 wherein said valve opening duration is controlled by anelectrically actuated valve.
 5. The method of claim 1 further comprisingoperating said internal combustion engine at a first spark angle advanceduring said first valve opening duration and operating said internalcombustion engine at a second spark angle during said second valveopening duration.
 6. The method of claim 1 further comprising combustinga lean air-fuel mixture until said predetermined operating condition. 7.The method of claim 1 further comprising adjusting the closing time ofat least an intake valve.
 8. The method of claim 1 wherein engine speedis held substantially constant.
 9. A method to control intake manifoldpressure for an internal combustion engine having a variable eventvalvetrain, the method comprising: during an engine start, operatingintake valves of said internal combustion engine asynchronous from saidinternal combustion engine's exhaust valves; operating said intakevalves synchronous with said exhaust valves after a predeterminedoperating condition; and reducing said intake manifold pressure byclosing a throttle located upstream of an intake manifold, andincreasing said first intake valve opening duration to produce a secondintake valve opening duration, in response to a predetermined engineoperating condition.
 10. The method of claim 9 wherein intake valveopening time is retarded from top-dead-center of the intake stroke. 11.The method of claim 9 wherein said predetermined engine operatingcondition is a number of combustion events.
 12. The method of claim 9wherein said predetermined engine operating condition is an amount oftime.
 13. The method of claim 9 wherein spark is advanced when saidintake manifold pressure is reduced.
 14. The method of claim 9 wherein alean air-fuel mixture is combusted after reducing said intake manifoldpressure.
 15. A method to control intake manifold pressure for aninternal combustion engine having a variable event valvetrain, themethod comprising: during an engine start, operating an internalcombustion engine at a first intake manifold pressure and a first intakevalve timing that increases heat transfer to an exhaust after treatmentdevice, said engine operating at said first intake manifold pressure andvalve timing until a first predetermined operating condition is met;operating said internal combustion engine at a second intake manifoldpressure and a second intake valve timing that increases heat transferfrom combusted gases to said internal combustion engine, said engineoperating at said second intake manifold pressure and said second intakevalve timing after said first predetermined condition is met and beforea second predetermined operating condition is met; and operating saidinternal combustion engine at a third intake manifold pressure and athird intake valve timing that reduces fuel consumption of said engine.16. The method of claim 15 wherein at least one of said first, second,or third operating condition is an amount of time.
 17. The method ofclaim 15 wherein said first and second intake valve timings are retardedsuch that intake valves open after top-dead-center compression stroke.18. The method of claim 17 wherein intake valve timing is advanced atsaid third intake valve timing.
 19. The method of claim 15 wherein sparkis retarded from top-dead-center compression stroke while said engine isoperated at said first intake manifold pressure and said first intakevalve timing.